November 10, 2013

Electric Fencing 101: Grounding

 

“Why are my animals pushing my electric fence? It was working fine in the spring, and the energizer is still clicking.”

 

Morgan Renner, Wyoming and Montana Territory Manager for Gallagher, one of the largest electric fencing companies in the world, says this may be the most common question he hears. The problem can usually be solved by checking the most overlooked component of electric fencing: how the system is grounded.

 

He tells his students at the many hands-on clinics he conducts throughout the west, “There are three things to remember about your electric fence: (1) Grounding, (2) Grounding and (3) Grounding!”

 

Morgan Explains

 

All energizers provide a pulse of energy that originates from their ‘hot’ terminal then travels down the fence line on a charged or ‘hot’ wire. Most users understand this aspect of electric fencing.  It’s fairly obvious that the hot wires can’t be touching a steel post or laying on the soil surface.  What’s not so obvious is that in the instant when an animal comes into contact with that charged wire, its body contains that energy but is not shocked… yet!  

 

In order to provide a shock and thus the respect for the fence, the energy must travel out of the animal’s feet, through the soil, into the energizer’s ground rods, then into the energizer’s ground terminal.  At that point, the circuit has been completed, and the animal receives the shock.  What I have described is an “all-hot” electric fence, shown below:

 

What might be wrong with using this type of system in most of west, let’s say in July and August? You guessed it. THE SOIL IS TO DRY!  An all-hot electric fence relies totally on adequate soil moisture to complete the circuit between the animal and the energizer’s ground system.

 

Designing a hot/ground fence

 

What can we do? Fortunately, there is an alternative design to use here in the arid west. Take the ground system right out to the animal. Connect the energizer’s ground terminal to the ground rods, and then connect the ground rods to a second wire in the fence line, making it a ground wire. We call this a “hot/ground” electric fence and the electron flow in this type of circuit is shown below:

As the animal attempts to penetrate the fence, it bridges the gap between the ‘hot’ and ‘ground’ wires and receives a shock. The electron flow is routed back to the energizer via a conductive wire, not blocked by dry soil. I can tell you from personal experience, this shock is about a hundred times more effective than one from a poorly grounded all-hot system!

 

Note that we usually recommend at least three, six–foot long galvanized steel ground rods, spaced at least ten feet apart, for these permanent electric fence systems. Think of the ground rods as an “antenna” that collects the energy to form the shock: The bigger the antenna, the greater the shock.

 

Steel posts or rebar are NEVER adequate grounds! They are either painted or rusted, both of which are very poor conductors. Also, don’t use anything other than galvanized steel in the ground system. Copper components, for example, can cause electrolysis and eventually corrode the system’s connections. Always use a quality galvanized clamp for ground rod AND fence wire connections.

 

There are a few more design considerations to think about when constructing this type of fence. Let’s go through them. The spacing of the fence wires becomes more important now, because we are trying to deliver the shock to the face of the animal. What happens when the shock is behind the brain of an animal? That’s right, they generally move forward through the fence.  Not good! 

 

Research and practical experience has shown the optimal hot/ground wire spacing for horses, cattle, calves, and bison to be ten inches maximum. For smaller species such as goats, sheep and hogs, six inch spacing or less works the best.

 

Another design consideration is what to do for gateways. Don’t forget to carry the ground across all your gates! You should use the same insulated cable buried in the same trench as you use to carry the hot to the other side. To be effective, the ground system must be connected throughout your fence, all the way to the end. This is illustrated here:

Photo of a 5-wire High-Tensile permanent electric fence used for bull control. The wire polarity from the top wire down is as follows: Hot / Ground / Hot / Ground / Hot.

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